UCLA

Chemical warfare agents (CWAs), in particular sarin pose a severe threat to both military personnel and civilians, necessitating the development of effective and efficient methods for their decontamination. The use of small, highly dispersed metal catalysts and single atom catalysts (SACs) supported on metal oxides has been a growingly appealing solution due to their superior reactivity and efficiency for the decomposition of CWAs. However, their dynamic stability and reactivity in reaction conditions are still subject of debate and insufficiently understood due to experimental limitation. This thesis aims to reconcile these shortcomings using Density Functional Theory, ab-initio thermodynamics theorem, and microkinetic modeling to help understand: (1) the dynamic stability of these highly dispersed metal single atom and nanoparticles, and (2) understand its implication towards the catalytic activity of CWA decomposition.Firstly, DFT calculations were performed to understand sarin’s base reactivity on plain, undoped rutile titanium dioxide, r-TiO2(110). We found that DMMP is a sufficient simulant to describe the chemistry of sarin as both molecules have strong binding on titania, with low reactivity and similar barrier to decompose. We then incorporate ab atomistic thermodynamics to explore the stability of Pt single atom (SA) on anatase TiO2(101). In reducing pretreatment, we show that Pt prefers adsorbed structure, occupying the surface oxygen vacancy. Using CO as probe molecule, we showcase the dynamic behavior of the Pt single atom and its intricacies in determining the rate determining intermediates during steady state reactions that is elusive to be determined by experiments alone. We then study the reactivity of GB and DMMP on Pt SA in oxidative conditions. Pt provides the thermodynamic drive to cleave P-X bond, while lowering the barrier to do so via a unique PtO4 planar-like structure. We then briefly study the role of highly dispersed Cu4 cluster with and without co-deposition of potassium to facilitate the decomposition of dimethyl methyl phosphonate, a simulant for sarin in controlled environments. We studied the role of highly dispersed Cu4 clusters, with and without potassium, in decomposing dimethyl methyl phosphonate (DMMP), a sarin simulant. Using NAP-XPS and DFT, we found that DMMP decomposes into highly reduced P-species at room temperature. Co-deposition of K and Cu4 clusters further improved reactivity, leaving no intact DMMP. The Cu4 clusters' fluxional nature enhances the exothermic cleavage of DMMP bonds, with reaction products binding preferentially to TiO2. Calculations of P 2p chemical shifts from various decomposition products align well with observed XPS spectra. Finally, we explored the stability of Pt6Ox supported on anatase TiO2(101) using the grand canonical basin hopping algorithm. Methanol reactivity studies showed that Pt single atoms facilitate methoxy formation, leading to CO2 + 2H2O and dioxomethylene pathways. Pt clusters oxidize to Pt6O10 in oxidative conditions, forming a stable bilayer structure with planar PtO4-subunits. This structure provides active O adatoms for oxidation reactions, crucial in methanol dehydrogenation. We found that reactivity of methanol translates well to the thermodynamic analysis of CWA decomposition, providing addition insights on potential catalyst performance for CWA degradation.